174 Ferguson and Merwin — The Ternary System. 



For the investigation of the wollastonite solid solu- 

 tions a study of the inversion temperatures was the only 

 feasible method since the diopside and akermanite solid 

 solutions are optically very similar except for the sign 

 and size of the optic axial angle. If no wollastonite solid 

 solutions exist within the region in question, then any 

 charge with composition lying within this region, if crys- 

 tallized at low temperatures, should consist of a mixture 

 of the two kinds of wollastonite solid solutions, and if 

 the temperature be raised above the inversion tempera- 

 ture of one kind of wollastonite solid solution, then there 

 should result a mixture of a pseudowollastonite solid 

 solution and the other wollastonite solid solution. If, 

 however, there is. an -area of solid solution, then for each 

 solid solution of intermediate composition there will be 

 a definite inversion temperature or interval of tempera- 

 ture. 11 The detection of an inversion temperature or 

 interval of temperature differing from that of the solid 

 solution of the bounding series would thus be proof of 

 an area of solid solution. The inversion temperatures 

 of the solid solutions of the two series are markedly dif- 

 ferent and thus enable one to obtain positive evidence on 

 this point. This evidence is given in Table IV, and also 

 some evidence upon the extent of the wollastonite solid 

 solution in the region beyond that covered by the pseu- 

 dowollastonite solid solutions. 



Table IV. 



Quenches which indicate the decomposition and inversion temperatures and 

 the extent of the area of the wollastonite solid solutions. 

 Time 

 Composition wt. % Temp. in Phases present 



CaO MgO Si0 2 °C. hours 



45 5 50 950 16 AU wollastonite 



Previous charge reheated 1220 0-5 All wollastonite 



Previous charge reheated 1250 0-4 Mainly changed to pseudo- 



wollastonite 

 44 6 50 880 16 Wollastonite with trace of 



pseudowollastonite 

 Previous charge reheated 1260 0-5 Unchanged 



Previous charge reheated 1290 0-5 Changed to pseudowollastonite 



43 7 50 950 16 Wollastonite 



Previous charge reheated 1328 45 Wollastonite and trace diopside 

 Previous charge reheated 1340 15 Now partly pseudowollastonite 

 41 8 51 950 15 Wollastonite only . 



1340 0-5 Eecrystallized wollastonite and 



diopside 

 1345 0-5 Eecrystallized wollastonite and 



diopside 

 11 This interval of temperature will be discussed later. 



